Do “Catch Reconstructions” really Implicate Overfishing?

A new paper led by Daniel Pauly of the University of British Columbia that found global catch data, as reported to the FAO, to be significantly lower than the true catch numbers. “Global fish catches are falling three times faster than official UN figures suggest, according to a landmark new study, with overfishing to blame.”

400 researches spent the last decade accumulating missing global catch data from small-scale fisheries, sport fisheries, illegal fishing activity and fish discarded at sea, which FAO statistics, “rarely include.”

“Our results indicate that the decline is very strong and is not due to countries fishing less. It is due to countries having fished too much and having exhausted one fishery after another,” Pauly says.

Despite these findings, Pauly doesn’t expect countries to realize the need to rebuild stocks, primarily because the pressures to continue current fishing effort are too strong in the developing world. But this study will allow researchers to see the true problems more clearly and hopefully inform policy makers accordingly.

We have had many different scientists comment on the paper:

Jump to Michel J. Kaiser’s response
Jump to David Agnew’s response
Jump to Ray Hilborn’s response
Jump to Martin Pastoors’s response
Jump to Karl-Michael Werner’s response

Comment by Michel J. Kaiser, Bangor University, @MicheljKaiser

Catch and stock status are two distinct measurement tools for evaluating a fishery, and suggesting inconsistent catch data is a definitive gauge of fishery health is an unreasonable indictment of the stock assessment process. Pauly and Zeller surmise that declining catches since 1996 could be a sign of fishery collapse. While they do acknowledge management changes as another possible factor, the context is misleading and important management efforts are not represented. The moratorium on cod landings is a good example – zero cod landings in the Northwest Atlantic does not mean there are zero cod in the water. Such distinctions are not apparent in the analysis.

Another key consideration missing from this paper is varying management capacity. European fisheries are managed more effectively and provide more complete data than Indian Ocean fisheries, for example. A study that aggregates global landings data is suspect because indeed landings data from loosely managed fisheries are suspect.

Finally the author’s estimated catch seems to mirror that of the official FAO catch data, ironically proving its legitimacy. “Official” FAO data is not considered to be completely accurate, but rather a proportionate depiction of global trends. Pauly’s trend line is almost identical, just shifted up the y axis, and thus fails to significantly alter our perception of global fisheries.

Michel J. Kaiser is a Professor of Marine Conservation Ecology at Bangor University. Find him on twitter here.


Comment by David Agnew, Director of Standards, Marine Stewardship Council

The analysis of such a massive amount of data is a monumental task, and I suspect that the broad conclusions are correct. However, as is usual with these sorts of analyses, when one gets to a level of detail where the actual assumptions can be examined, in an area in which one is knowledgeable, it is difficult to follow all the arguments.  The Antarctic catches “reconstruction” apparently is based on one Fisheries Centre report (2015 Volume 23 Number 1) and a paper on fishing down ecosystems (Polar Record; Ainley and Pauly 2014). The only “reconstruction” appears to be the addition of IUU and discard data, all of which are scrupulously reported by CCAMLR anyway, so they are not unknown. But there is an apparent 100,000 t “unreported” catch in the reconstruction in Figure 3, Atlantic, Antarctic (48). This cannot include the Falklands (part of the Fisheries Centre paper) and it is of a size that could only be an alleged misreporting of krill catch in 2009. This is perhaps an oblique reference to concerns that CCAMLR has had in the past about conversion factors applied to krill products, or perhaps unseen (net-impact) mortality, but neither of these elements have been substantiated, nor referenced in the supporting documentation that I have seen (although I could not access the polar record paper).

The paper does not go into much detail on these reasons for the observed declines in catches and discards, except to attribute it to both reductions in fishing mortality attendant on management action to reduce mortality and generate sustainability, and some reference to declines in areas that are not managed. It is noteworthy that the peak of the industrial catches – in the late 1990s/early 2000s – coincidentally aligns with the start of the recovery of many well managed stocks. This point of recovery has been documented previously (Costello et al 2012; Rosenberg et al 2006; Gutierrez et al 2012) and particularly relates to the recovery of large numbers of stocks in the north Pacific, the north Atlantic and around Australia and New Zealand, and mostly to stocks that are assessed by analytical models. For stocks that need to begin recovery plans to achieve sustainability, this most often entails an overall reduction in fishing effort, which would be reflected in the reductions in catches seen here. So, one could attribute some of the decline in industrial catch in these regions to a correct management response to rebuild stocks to a sustainable status, although I have not directly analyzed the evidence for this. This is therefore a positive outcome worth reporting.

The above-reported inflection point is also coincident with the launch of the MSC’s sustainability standard. These standards have now been used to assess almost 300 fisheries, and have generated environmental improvements in most of them (MSC 2015). Stock sustainability is part of the requirements of the standard, and previous analyses (Gutierrez et al 2012Agnew et al 2012) have shown that certified fisheries have improved their stock status and achieved sustainability at a higher rate than uncertified fisheries. The MSC program does not claim responsibility for the turn-around in global stocks, but along with other actions – such as those taken by global bodies such as FAO, by national administrations, and by industry and non-Governmental Organisations – it can claim to have provided a significant incentive for fisheries to become, and then remain, certified.

David Agnew is the Director of Standards at the Marine Stewardship Council, the largest fishery sustainability ecolabel in the world. You can follow MSC on twitter.


Comment by Ray Hilborn, University of Washington, @hilbornr

This paper tells us nothing fundamentally new about world catch, and absolutely nothing new about the status of fish stocks.

It has long been recognized that by-catch, illegal catch and artisanal catch were underrepresented in the FAO catch database, and that by-catch has declined dramatically.

What the authors claim, and the numerous media have taken up, is the cry that their results show that world fish stocks are in worse shape than we thought. This is absolutely wrong. We know that fish stocks are stable in some places, increasing in others and declining in yet others.

Most of the major fish stocks of the world, constituting 40% of the total catch are scientifically assessed using a mixture of data sources including data on the trends in abundance of the fish stocks, size and age data of the fish caught and other information as available. This paper really adds nothing to our understanding of these major fish stocks.

Another group of stocks, constituting about 20% of global catch, are assessed using expert knowledge by the FAO. These experts use their personal knowledge of these fish stocks to provide an assessment of their status. Estimating the historical unreported catch for these stocks adds nothing to our understanding of these stocks.

For many of the most important stocks that are not assessed by scientific organizations or by expert opinion, we often know a lot about their status. For example; abundance of fish throughout almost all of South and Southeast Asia has declined significantly. This is based on the catch per unit of fishing effort and the size of the individuals being caught. Estimating the amount of other unreported catches does not change our perspective on the status of these stocks.

In the remaining fisheries where we know little about their status, does the fact that catches have declined at a faster rate than reported in the FAO catch data tell us that global fisheries are in worse shape than we thought? The answer is not really. We would have to believe that the catch is a good index of the abundance.

Looking at Figure 1 of the Pauly and Zeller paper we see that a number of major fishing regions have not seen declines in catch in the last 10 years. These areas include the Mediterranean and Black Sea, the Eastern Central Atlantic, the Eastern Indian Ocean, the Northwest Pacific and the Western Indian Ocean. Does this mean that the stocks in these areas are in good shape, while areas that have seen significant declines in catch like the Northeast Atlantic, and the Northeast Pacific are in worse shape?

We know from scientific assessments that stocks in the Mediterranean and Eastern Central Atlantic are often heavily overfished – yet catches have not declined.

We know that stocks in the Northeast Pacific are abundant, stable and not overfished, and in the Northeast Atlantic are increasing in abundance. Yet their catch has declined.

Total catch, and declines in catch, are not a good index of the trends in fish stock abundance.

Pauly and Zeller have attempted to estimate the extent of unreported catch for all the fish stocks of the world. For any individual stock in the U.S. the hardest part of doing the stock assessment is often estimating the total catch. Historical discards are often unreported, species were often lumped in the historical catch data, recreational catch was poorly estimated, and illegal catch totally unreported. Scientists can spend months trying to reconstruct these data for an individual stock and it is recognized that these estimates may not be reliable. Pauly and Zeller’s attempt to do this for thousands of global stocks with a consultant spending perhaps a few months to cover every fishery in an individual country just cannot be very reliable.

We need to move beyond trying to understand the historical fish catches, and instead concentrate on understanding the status of fish stocks at present. If all the effort that had been spent in trying to estimate historical catches by Pauly and Zeller had instead been devoted to analysis of what we know about the status of a sample of fish stocks in different places, we would know much more about the status of world fisheries.

Ray Hilborn is a Professor in the School of Aquatic and Fishery Sciences at the University of Washington. Find him on twitter here: @hilbornr


Comment from Martin Pastoors, Chief Science Officer, Pelagic Freezer-trawler Association (PFA)

After considering their methodology, these are some concerns with the analysis in regards to Dutch fishery operations:

“Unreported” catches were estimated from the ICES working group reports that often refer to a category called “unallocated” catches. They have interpreted this unallocated catch as unreported catch (whereas in fact they often consist of differences in calculation methods from dead weight to live weight). These unallocated catches were first split into unallocated catches by county (proportional to the size of the reported catch) and then extrapolated for the years where unallocated catches were not available (basically 1950-1990). So this is in fact inflating a somewhat random number to the largest part of the time series.

The same approach is applied for the discard data, all the way extrapolated back to 1950.

They did not explain how they attributed the Dutch catch to the Dutch EEZ. I think this is pointless anyway because a large part of the Dutch catch is taken outsize of the EEZ and even outside of the North Sea.

There are some pretty normative statements about the fishery that should have no role in a data report, e.g. “they are powerful and destructive due to relying heavily on beam trawling”

The data that has been compiled is not presented in the report, nor are the conversion factors used. It is impossible to reconstruct what data they have taken from where and what ‘data’ is based on extrapolations and what is based on time series from other reports.

So all in all, I think we can say that they have spent a lot of effort to recreate catch data largely based on undocumented extrapolations that are missing the point with regards to Dutch fisheries (because Dutch fisheries largely take place outside the Dutch EEZ).

Martin Pastoors is the chief science officer at the Pelagic Freezer-trawler Association (PFA).

Comment by Karl-Michael Werner, University of Bergen, Norway

Pauly and Zeller’s conclusion that global catches were previously underestimated is not surprising given the implicit understanding that FAO catch estimations have always omitted factors like discards and recreational fishing. Their efforts to include these pieces of missing data were impressive and reputable. However their interpretations of the results are questionable on a few key points:

First, there is not appropriate consideration given to the potential impact on global catch data of just a few key species. In a related study from the Sea Around Us, the Peruvian Anchoveta and Alaska Pollock fisheries accounted for a decline of 10 million tons in global catch from 1996-2010, which is almost half of the reconstructed decline during that period. Comparatively, “Other species” only accounted for 6 million tons in the same study. This displays the relative impact a major fishery can have on global catch data sets, even a data set as comprehensive as Pauly and Zeller’s. Implications for global stocks are thus less valid because fluctuations in either of these two fisheries could show misrepresentative trends. Additionally, discards fell by 5 million tons between 1996 and 2010, which should be highlighted as a positive trend and not as part of reduced catches due to overfishing.

Secondly, it should be noted that Peru enforces a quota management system for the Anchoveta fishery and indeed catches declined in accordance with this mandate. Unfortunately Pauly and Zeller only include the United States, northwest Europe, Australia and New Zealand as countries utilizing fisheries quota management where catch reductions are on purpose.

It appears that the years 1996, which reported temporarily high catches, and 2010, with temporarily low catches, were arbitrarily chosen in order to produce a specific trend line. 1996 and 2010 represent a local high and a local low, which do not allow for a serious comparison of global catch. These fluctuations could be due to environmental changes and there is little evidence linking them directly to overfishing.

Lastly, catches are not always a fair representation of stock status. This potential pitfall has been documented before (Branch et al, 2011; Daan et al., 2011) but is not appropriately considered by Pauly and Zeller in this paper. Understandably there are many global fisheries that only have catch data with which to draw stock status conclusions, but then how can such fisheries be grouped with data-complete fisheries in a single analysis? Catches were higher than expected, which could suggest fisheries are more productive than expected. According to Pauly & Zeller, catches were high because stocks were overfished, but then catches went down due to overfishing as well. This is paradox; how are catch curves supposed to look like in order to be not considered as overfished then?

Karl-Michael Werner is a PhD candidate at the University of Bergen, Norway
Posted in Uncategorized.


  1. You are insane, I am a commercial fishermen off California. I have the fishing vessel pioneer, out of monterey bay. I have to pay for a federal observer to go fishing with me every time. 530.00 dollars a day pluss I have to pay the federal government 8 percent of everything I gross. I also have to pay for a boat tracking system. On top of everything, they put cameras on my boat too.
    Where does the insanity stop. The fisherman are going broke.

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